The invention relates in general to the operation of a refrigeration system, and more specifically to the control of the evaporator and condenser fans in a refrigeration system.
Refrigeration systems generally include a refrigerant circuit including a compressor, a condenser, a main throttling device, and an evaporator. Vapor refrigerant is delivered to the compressor where the temperature and pressure of the vapor refrigerant is increased. The compressed, vapor refrigerant is then delivered to the condenser where heat is removed from the vapor refrigerant in order to condense the vapor refrigerant into liquid refrigerant. Heat is removed from the vapor refrigerant by circulating air over the condenser.
Air is circulated over the condenser by a condenser fan. The condenser fan in refrigeration systems is commonly powered by cycling between a power source and a ground, i.e. by turning the fan on and off. When the condenser fan is cycled equally between on and off, the condenser fan consumes half as much power as when the condenser fan is always on.
From the condenser, the liquid refrigerant is delivered to a main throttling device The main throttling device restricts the flow of the liquid refrigerant by forcing the liquid through a small orifice in order to decrease the pressure of the liquid, causing the liquid to evaporate. Upon exiting the main throttling device, the liquid refrigerant is in the form of liquid refrigerant droplets.
From the main throttling device, the liquid refrigerant droplets are delivered to the evaporator. The evaporator is located within or in thermal communication with the space to be conditioned by the refrigeration system. As air circulates over the evaporator, the liquid refrigerant droplets continue to evaporate and absorb heat from the air in order to cool the air. The cooled air is circulated through the conditioned space to cool the masses within the conditioned space. As the liquid refrigerant droplets absorb heat, the liquid refrigerant droplets vaporize. To complete the refrigeration cycle, the vapor refrigerant is delivered from the evaporator back to the compressor.
Air is circulated over the evaporator and through the conditioned space by one or more evaporator fans. The evaporator fans in refrigeration systems are physically located in the air stream of the air being circulated through the conditioned space. Due to the physical location of the evaporator fans, the power supplied to the evaporator fans is ultimately added to conditioned space as unwanted heat. The unwanted heat added to the conditioned space by the evaporator fans must be compensated for by increasing the amount of cooling that the refrigeration system must do. Thus, evaporator fans require the refrigeration system to consume power to compensate for the unwanted heat, in addition to the power required to operate the evaporator fans. The net effect is that the electric power used to move air within the conditioned space is ultimately counted twice as non-cooling power.
In refrigeration systems with two-speed evaporator fans, the higher speed is typically used when the conditioned space is above freezing, while the lower speed is used when the conditioned space is below freezing. When keeping the conditioned space above freezing, it is more acceptable to add unwanted heat to the conditioned space. As a result, the evaporator fans can be operated at the higher speed, even though the evaporator fans emit more heat at the higher speed. When keeping the conditioned space below freezing, it is less acceptable to add unwanted heat to the conditioned space. As a result, the evaporator fans are operated at the lower speed in order to minimize the heat generated by the evaporator fans.
The use of two-speed condenser and evaporator fans in refrigeration systems has several limitations. Since the fans must be operated at one of two speeds, the fans cannot be operated at their most energy efficient speed. This results in more power being consumed by the fans and higher operating costs for the refrigeration system. Moreover, when the refrigeration system requires more power to operate, the refrigeration system consumes more non-renewable fossil fuel and the refrigeration system creates more air pollution. Specifically regarding the evaporator fans in refrigeration systems, since the fans must be operated at one of two speeds, more unwanted heat is often added to the conditioned space than is necessary. When more unwanted heat is added to the conditioned space, the time period for the refrigeration system to cool the conditioned space to within the desired temperature range is extended. Moreover, when the evaporator fans are operated at the higher speed, more air is circulated through the conditioned space which may result in the undesirable dehydration of the goods stored within the conditioned space.
The present invention provides a method and apparatus for controlling continuously-variable speed evaporator and condenser fans in a refrigeration system in order to minimize the power consumed by the evaporator and condenser fans, in order to minimize the unwanted heat added to the conditioned space by the evaporator fans, and in order to minimize the quantity of air circulated through the conditioned space by the evaporator fans to reduce the dehydration of the goods stored within the conditioned space.
In one embodiment of the invention, the apparatus is a refrigeration system including a refrigerant circuit defined by a compressor, a condenser, a throttling device, and an evaporator. The refrigeration system includes at least one evaporator fan and a controller coupled to the evaporator fan. The controller includes a variable frequency drive unit for providing variable frequency power to the evaporator fan. By virtue of this design, the speed of the evaporator fan can be precisely controlled so that the fan only operates at the desired speed, thus saving power, reducing unwanted heat, and reducing dehydration of the goods.
In another embodiment of the invention, the refrigeration system includes at least one condenser fan and a controller coupled to the condenser fan. The controller includes a variable frequency drive unit for providing variable frequency power to the condenser fan.
In one embodiment of the method of the invention, the speed of at least one evaporator fan is controlled in a refrigeration system including a compressor, a condenser, a throttling device, and an evaporator. The method includes providing a desired temperature for a conditioned space, measuring temperature at the inlet to the evaporator, and measuring temperature at the outlet to the evaporator. The method also includes calculating an actual temperature differential and adjusting an evaporator fan speed based on the desired temperature differential and the actual temperature differential.
In another embodiment of the method of the invention, the speed of at least one condenser fan is controlled. The method includes providing a condenser temperature threshold value and measuring an actual temperature of the condenser. The method also includes adjusting a condenser fan speed based on the condenser temperature threshold value and the actual temperature.
Other features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following description, claims, and drawings.